The present invention relates to semiconductor packaging, and, more particularly, to a molding apparatus for molding semiconductor devices.
Semiconductor packaging is the final stage in semiconductor device fabrication, where an integrated circuit (IC) is encapsulated with a material such as plastic or resin. In many types of packages, a lead frame is used for providing electrical interconnections to a semiconductor die. The semiconductor die is attached to the lead frame and bonding pads of the semiconductor die are electrically connected to leads of the lead frame, typically with wires, by a wire-bonding process. The leads allow for electrical interconnections between the semiconductor die and external circuitry.
A lead frame assembly (lead frame with attached die and bond wires) is placed in a cavity defined by mold chases (top and bottom mold chases), and the molding compound is poured or injected into the cavity. The final packaged semiconductor device is formed by separating the mold chases and performing appropriate processes on the molded lead frame such as trimming and forming of leads.
FIG. 1 is a schematic diagram illustrating a step in a conventional semiconductor assembly or packaging process. FIG. 1 shows a lead frame structure or array 100 that includes a plurality of individual lead frames 102. In this case, the lead frames 102 are used to form dual-in-line packages (DIP). Each individual lead frame 102 includes a die pad on which a semiconductor die 104 is attached and an opposing pair of rows of leads 106. The semiconductor dies 104 are electrically connected to the leads 106 of a respective lead frame 102 with bond wires 108. The leads 106 may extend beyond the mold compound or encapsulation material (not shown) in order to serve as the means for external electrical connections between the semiconductor die 104 and external circuitry. The lead frame array 100 with attached dies 104 is placed in a mold chase so that an encapsulation process may be performed.
FIG. 2 is a schematic view of a bottom mold chase 202 of a conventional molding apparatus 200, a top mold chase being a mirror image of the bottom chase 202. The top and bottom mold chases are configured to align with each other. The bottom mold chase 202 and the top mold chase include one or more cavities 204 for receiving the lead frame assembly (lead frame array 100 and dies 104) of FIG. 1, where the individual lead frames 102 are received within respective ones of the cavities 204 of the bottom mold chase 202. The bottom mold chase 202 includes a runner 206 and gates 208 at each of the cavities 204.
A mold compound is introduced into the cavities 204 via the runner 206 and gates 208. When the mold compound hardens, the top and bottom mold chases are separated and the encapsulated lead frame assembly is removed. Individual semiconductor devices are then formed by separating the molded semiconductor dies from each other.
One of the disadvantages with the conventional molding apparatus 200 is that the individual cavities 204 are spaced from each other so that the actual design of the mold chase is inefficient. The space occupied by the runner 206 and gates 208 also results in a low density lead frame array or strip design. As seen in FIG. 1, the lead frame array 100 has two vertical columns of lead frames 102 in which the lead frames 102 are spaced from adjacent lead frames in both the X and Y directions. Further, the mold compound only flows to the individual cavities 204 but does not flow between cavities 204, i.e., from one cavity into an adjacent cavity. Also, the mold compound flows down the single runner 206 in one direction and must change direction 90° to flow into the cavities 204. The mold chase 202 also has a gate 208 for each cavity 204 and high pressure is needed to insure the mold flows into each of the cavities 204.
It would be advantageous to provide a molding apparatus that accommodates more lead frames and allows for uniform mold flow but with lower pressure.